The present invention relates to aircraft engine thrust reverser actuation systems and, more particularly, to a decoupler that is used to limit the torque in an aircraft thrust reverser drive train that is driven by a single power drive unit.
When a jet-powered aircraft lands, the landing gear brakes and aerodynamic drag (e.g., flaps, spoilers, etc.) of the aircraft may not, in certain situations, be sufficient to slow the aircraft down in the required amount of runway distance. Thus, jet engines on most aircraft include thrust reversers to enhance the braking of the aircraft. When deployed, a thrust reverser redirects the rearward thrust of the jet engine to a generally or partially forward direction to decelerate the aircraft. Because at least some of the jet thrust is directed forward, the jet thrust also slows down the aircraft upon landing.
Various thrust reverser designs are commonly known, and the particular design utilized depends, at least in part, on the engine manufacturer, the engine configuration, and the propulsion technology being used. Thrust reverser designs used most prominently with jet engines fall into three general categories: (1) cascade-type thrust reversers; (2) target-type thrust reversers; and (3) pivot door thrust reversers. Each of these designs employs a different type of moveable thrust reverser component to change the direction of the jet thrust.
Cascade-type thrust reversers are normally used on high-bypass ratio jet engines. This type of thrust reverser is located on the circumference of the engine""s midsection and, when deployed, exposes and redirects air flow through a plurality of cascade vanes. The moveable thrust reverser components in the cascade design includes several translating sleeves or cowls (xe2x80x9ctranscowlsxe2x80x9d) that are deployed to expose the cascade vanes.
Target-type reversers, also referred to as clamshell reversers, are typically used with low-bypass ratio jet engines. Target-type thrust reversers use two doors as the moveable thrust reverser components to block the entire jet thrust coming from the rear of the engine. These doors arc mounted on the aft portion of the engine and may form the rear part of the engine nacelle.
Pivot door thrust reversers may utilize four doors on the engine nacelle as the moveable thrust reverser components. In the deployed position, these doors extend outwardly from the nacelle to redirect the jet thrust.
The primary use of thrust reversers is, as noted above, to enhance the braking of the aircraft, thereby shortening the stopping distance during landing. Hence, thrust reversers are usually deployed during the landing process to slow the aircraft. Thereafter, when the thrust reversers are no longer needed, they arc returned to their original, or stowed, position. In the stowed position, the thrust reversers do not redirect the jet engine""s thrust.
The moveable thrust reverser components in each of the above-described designs are moved between the stowed and deployed positions by actuators. Power to drive the actuators may come from a dual output power drive unit (PDU), which may be electrically, hydraulically, or pneumatically operated, depending on the system design. A drive train that includes one or more drive mechanisms, such as flexible rotating shafts, may interconnect the actuators and the PDU to transmit the PDU""s drive force to the moveable thrust reverser components.
Each of the above-described thrust reverser system configurations is robustly designed and is safe and reliable. Nonetheless, analysis has shown that secondary damage to various portions of the thrust reverser system may result under certain postulated circumstances. For example, if one of the actuators coupled to one of the PDU outputs becomes jammed, it is postulated that all of the drive force supplied from the PDU would be concentrated, via the synchronization mechanisms, on the jammed actuator. This postulated condition may result in damage to the actuator system components, including the PDU, actuators, drive mechanisms, or the moveable thrust reversers components. Repairing such damage can be costly and result in aircraft down time. One solution is to use stronger components, but this increases the cost and/or weight of the thrust reverser system. Another solution is to include numerous, independently operated torque limiters or decouplers in each drive train coupled to the PDU outputs. However, this solution may also increase system cost and/or weight.
Accordingly, there is a need for a thrust reverser system that improves upon one or more of the drawbacks identified above. Namely, a system that reduces the likelihood of component damage if the thrust reverser system fails, for example, by a jammed actuator, without significantly increasing the cost and/or the weight of the thrust reverser system components. The present invention addresses one or more of these needs.
The present invention provides a system and method that sequentially decouples a thrust reverser system power drive unit from two or more loads that are coupled to a single output shaft in the event a torque magnitude is reached between the power drive unit and one of the loads.
In one embodiment, and by way of example only, a thrust reverser control system includes a motor, at least two drive mechanisms, at least two actuators, and a torque decoupler. The motor has an output shaft and is operable to supply a drive force. The drive mechanisms are each coupled to receive the drive force. Each actuator assembly is coupled to at least one of the drive mechanisms and is operable to move, upon receipt of the drive force, between a stowed position and a deployed position. The torque decoupler is coupled between the motor output shaft and two of the drive mechanisms and includes a first output section and a second output section. The first output section is coupled to the motor output shaft and is operable to (i) decouple the motor from one of the drive mechanisms upon a first torque magnitude being reached in the first output section and (ii) engage the second output section a time period after the first torque magnitude is reached. The second output section is coupled to the motor output shaft and is operable to (i) decouple the motor from the other drive mechanism upon a second torque magnitude being reached in the second output section and (ii) engage the first output section a time period after the second torque magnitude is reached.
In another exemplary embodiment, a power drive unit includes a motor, a first output section, and a second output section. The motor has an output shaft and is operable to supply a drive force to at least a first load and a second load. The first and second output section are coupled to the motor output shaft. The first output section is operable to (i) decouple the motor from the first load upon a first torque magnitude being reached in the first output section and (ii) engage the second output section a time period after the first torque magnitude is reached. The second output section is operable to (i) decouple the motor from the second load upon a second torque magnitude being reached in the second output section and (ii) engage the first output section a time period after the second torque magnitude is reached.
In yet another exemplary embodiment, a torque decoupler assembly operable to decouple at least a first and a second load from a single motor output shaft includes a first output section and a second output section. The first output section is adapted to couple to the motor output shaft and is operable to (i) decouple the motor from the first load upon a first torque magnitude being reached in the first output section and (ii) engage the second output section a time period after the first torque magnitude is reached. The second output section is adapted to couple to the motor output shaft and is operable to (i) decouple the motor from the second load upon a second torque magnitude being reached in the second output section and (ii) engage the first output section a time period after the second torque magnitude is reached.
Other independent features and advantages of the preferred thrust reverser system and torque decoupler will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.